Inorganic antireflective coatings are used to counteract the overexposure which can occur with structures that reflect exposure light. To illustrate, referring to FIG. 1, there is shown a partially completed integrated circuit. Field oxide regions 11 have been formed in and on a semiconductor substrate 10. Polysilicon or polycide gate electrodes 14 have been formed. A dielectric layer 16 covers the gate electrodes. An oxide layer 20, typically borophosphosilicate glass (BPSG), is grown over the dielectric layer 16. A layer of photoresist is coated over the oxide layer 20 and patterned to form a mask. Because of the reflective surface of the oxide layer 20 and the intensity of the deep ultraviolet light 22 used, the light rays 22 are reflected onto the photoresist layer (PR) causing overexposure. The resulting photoresist mask has a notch in it. Therefore, when subsequent layers are patterned according to the photoresist mask and etched, a notch 24 will result, as shown in top view in FIG. 2.
In order to counteract this problem, an antireflective coating (DARC) 24 is commonly used, as shown in FIG. 3. The DARC 24 is generally composed mostly of Si, with the next most abundant element being O, and the balance N. Once exposure is complete, the DARC is removed using wet etching.
Wet etching solutions significantly, and sometimes even preferentially, attack silicon oxides such as BPSG. Accordingly, when performing wet etches, excessive amounts of the underlying oxide layer 20 may be removed, especially when using BPSG. When this occurs, as illustrated in FIG. 4, an overhang of the DARC 24 is produced. This overhang can interfere or react with subsequent depositions, for example, when layers are deposited into a cavity over which the DARC 24 extends.
Prior art etching techniques refer to the use of particular solvents for etching in certain circumstances. Wei et al., U.S. Pat. No. 5,449,639, refers to a method of metal etching using a solution of hydrogen peroxide, ammonia, and water. Izumi et al., U.S. Pat. No. 5,022,961, refers to etching thermal oxide films of silicon with hydrofluoric acid (HF) or other halide-containing species in combination with alcohol. Maeda et al., U.S. Pat. No. 4,746,397 describes etching SiO.sub.2 films with the use of a flourine-containing species and an alcohol, ketone or carboxylic acid.
What are still needed, however, are methods designed for the selective etching of DARCs while preventing or minimizing the etching of the adjacent oxide.